The predominant involvement of the respiratory system in COVID-19 pathogenesis mainly stems from the mode of entry of the virus into the host, i.e., respiratory tract, and also owing to the high expression of angiotensin-converting enzyme 2 (ACE2), the classical receptor to which the viral spike protein ligand can engage with, on the respiratory and the gastrointestinal epithelia. This evidence concerns the gene ACE2 and COVID-19.